A.2 Health Reporting Areas
A.2.1 Introduction
Resolving geographic units that do not neatly coincide is a common problem in spatial data analysis. This method attempts to conflate King County Health Reporting Areas (HRAs) to US Census tracts. In the cases where a given tract with entirely within a HRA, that tract receives the HRA’s ID. Where a given tract overlaps multiple HRAs block-level census data is used to determine which HRA ID to assign to the tract.
A.2.2 Census Block Counts
This method provides three alternatives of block-level counts that can be used:
- Population
- Housing Units
- Population in Housing Units
A.2.3 The Algorithm
The following actions are performed in this method:
- Centroids of the census block polygons are calculated (
class = SpatialPointsDataFrame) - HRA IDs are passed to the block centroid using a spatial overlay method (
sp::over()) - Blocks are aggregated into tracts and the count variables (
POP,HU,POPHU) are summed - For each count variable, the HRA ID with the highest sum is assigned to each tract